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Chuan Hou, Spero C. Nicholas; The cortical sources of amblyopic suppression: An EEG source imaging study. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6459.
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© ARVO (1962-2015); The Authors (2016-present)
Persistent suppression of visual inputs from the amblyopic eye by the dominant eye is a key factor in the development of amblyopia during early childhood. Amblyopic suppression is thought to occur in primary visual cortex (V1). Here we used EEG source imaging to investigate neural activities related to interocular suppression at different levels of the visual cortical hierarchy in human adult amblyopia, compared with normal-vision observers.
Using dichoptic presentation, 128 channel EEG responses were recorded from groups of strabismic and anisometropic amblyopes and normal-vision observers with Vernier-offset stimuli at 1Hz in one eye when the other eye was either patched or open but viewing a blank screen. All participants had structural and functional MRI scans to define the cortical regions of interest and build a model of the head for cortical source imaging. The responses from the stimulated eye were compared in conditions when the un-stimulated eye was either patched or open within each group and across groups.
In strabismic amblyopes, the scalp topography showed a strong suppression in the occipital area around 165 ms after stimulus onset when stimulating the amblyopic eye with the dominant eye open to a blank screen. However, such suppression was eliminated when the dominant eye was patched. The cortical sources of suppression were found along the dorsal stream, where the higher visual cortex (V2d, V3d and V3a) had stronger interocular suppression than V1. Anisometropic amblyopes showed overall weaker interocular suppression when compared with strabismic amblyopes, and their cortical sources of suppression were found more in the ventral rather than the dorsal stream. The suppression amount was also larger in higher visual cortex (V2v, V3v, hV4) than in V1. Anisometropic amblyopes, unlike strabismic amblyopes, showed a similar pattern of interocular suppression to that of normal-vision observers.
Our study showed that amblyopic suppression occurs whenever the dominant eye is open, even without stimulation. Strabismic and anisometropic amblyopia have distinct patterns of interocular suppression, in which the strabismic suppression occurs more prominently in the dorsal stream while the anisometropic suppression occurs more prominently in the ventral stream. Both types of amblyopia have stronger interocular suppression in higher visual cortex than in V1.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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